TAP studies of CO oxidation over CuMnO and Au/CuMnO catalysts

The mechanism of CO oxidation reactions over undoped and gold-doped CuMnOX (Hopcalite) catalysts has been examined using a temporal analysis of products (TAP) reactor. Gold doping has been found to increase the activity of the mixed oxide catalyst significantly; however, using consecutive pulsing TAP experiments, the presence of gold was not found to affect the contribution of the Langmuir–Hinshelwood mechanism. Conversely, gold doping was found to promote the Mars van Krevelen mechanism. Using CO and O2 multi-pulse TAP experiments, the gold was found to modify the catalyst surface such that it stores much more oxygen that is active for the CO oxidation. The CO multi-pulse experiments indicated that two distinct types of active oxygen species were found to be involved in the CO oxidation. One type was observed in a similar amount on both doped and undoped catalysts and was associated with mixed oxide, while the second type was only found on the gold-doped catalyst and was therefore clearly associated with the presence of gold on the catalyst surface. The latter was found to be much less active than the oxygen inherent to the oxide but was at a concentration of approximately 10 times larger leading to the enhanced activity observed on gold doping.